The present invention relates to an adjustable valve locking system for valves of the type having a rotatable drive or actuating mechanism for a valve spindle. (e.g., a gate valve). In such systems, a lock housing is secured to a valve housing while an annular member surrounds a valve spindle within the lock housing and is rotatable by the actuating mechanism. A connection is provided between the annular member and the valve spindle whereby rotation of the annular member will cause axial movement of the valve spindle and a valve element carried thereby. This connection may comprise either a splined connection in the case where the spindle rotates or may comprise a threaded connection in the case of a non-rotating or spindle. In either case, the spindle moves in an axial direction within the surrounding annular member as the annular member rotates. A ring threadedly engages the outer periphery of the aforesaid annular member; while a radially-movable locking bolt in the lock housing is moved into engagement with the aforesaid ring to lock the same against axial movement while preventing rotation of the annular member to lock the valve spindle in a selected axial position. The locking bolt is normally movable between locking and unlocking positions by means of a lock cylinder actuated by a removable key. When the aforesaid locking bolt is out of locking engagement with the aforesaid threaded ring, it will move axially upwardly or downwardly due to a rectilinear guidance system such that the valve spindle is free to move until the axially-movable ring moves into position where it can be engaged by the locking bolt to hold it in position.
In one type of prior art locking system of the type described above, the valve can be locked only in its open and closed positions. Lock cylinders are usually used with such locking systems, the key for the lock cylinder being adapted to be withdrawn only when the lock is in a required locking position.
In prior art locking systems of this type the locking positions are preset and cannot be subsequently changed without considerable revision (e.g., to make a valve previously lockable in the open position now lockable in the closed position, or vice versa). Prior art locking systems of this type also have other disadvantages. For example, there may be a considerable difference between the required locking position and the actual locking position in the case of preset positions of this kind. This is due to the cumulative effect of different production tolerances in the case where the locking system is mass produced.